The present invention relates generally to interface devices for allowing humans to interface with computer systems, and more particularly to computer interface devices that allow the user to provide input to computer systems and allow computer systems to provide force feedback to the user.
Users interact with computer systems for a variety of reasons. A computer system typically displays a visual environment to a user on a display output device. Using an interface device, a user can interact with the displayed environment to perform functions and tasks on the computer, such as playing a game, experiencing a simulation or virtual reality environment, using a computer aided design system, operating a graphical user interface (GUI), or otherwise influencing events or images depicted on the screen. Common human-computer interface devices used for such interaction include a joystick, mouse, trackball, stylus, tablet, pressure-sensitive ball, or the like, that is connected to the computer system controlling the displayed environment. Typically, the computer updates the environment in response to the user's manipulation of a user-manipulatable physical object such as a joystick handle or mouse, and provides visual and audio feedback to the user utilizing the display screen and audio speakers. The computer senses the user's manipulation of the user object through sensors provided on the interface device that send locative signals to the computer. For example, the computer displays a cursor or other graphical object in a graphical environment, where the location of the cursor is responsive to the to the motion of the user object. The user can thus control the location of the cursor by moving the user object.
In some interface devices, tactile and/or haptic feedback is also provided to the user, more generally known as "force feedback." These types of interface devices can provide physical sensations which are felt by the user manipulating a user manipulable object of the interface device. For example, the Force-FX joystick controller from CH Products, Inc. and Immersion Corporation may be connected to a computer and provides forces to a user of the controller. Other systems might use a force feedback mouse controller. One or more motors or other actuators are coupled to the joystick and are connected to the controlling computer system. The computer system controls forces on the joystick in conjunction and coordinated with displayed events and interactions by sending control signals or commands to the actuators. The computer system can thus convey physical force sensations to the user in conjunction with other supplied feedback as the user is grasping or contacting the joystick or other object of the interface device. For example, when the user moves the manipulatable object and causes a displayed cursor to interact with a different displayed graphical object, the computer can issue a command that causes the actuator to output a force on the user object, conveying a feel sensation to the user.
The use of a user-controlled cursor in a graphical environment is well suited for use with force feedback. For example, a cursor that is moved into a displayed surface will be felt as a collision into a hard surface to the user because the actuator pushes back on the user object as the cursor is pushed against the displayed surface. Or, a user may move a cursor into a defined region on the graphical display and feel a vibration force on the user object as confirmation that the cursor is positioned within that region.
Other embodiments of force feedback systems do not involve control of a cursor. For example, a force feedback joystick can be used in video game applications, such as to fly a simulated aircraft. Sensors on the joystick allow the user to influence motion of the airplane, while actuators on the joystick allow the user to feel realistic force sensations. For example, the aircraft is flown into a simulated storm, where the host computer issues a force command that causes the actuators to create a feel of turbulence. This turbulence shakes the joystick in a convincing manner coordinated with the simulated storm.
A current problem with the prior art force feedback interfaces is that certain force sensations imposed by the actuator(s) on the user object cause a graphical object to move in undesired ways. For example, a vibration sensation imposed on a cursor control interface may cause the user object to shake. This, in turn, causes the cursor to shake or "jitter" on the screen because the cursor position is based on sensor readings describing the position of the user object. Such vibrations may cause the user difficulty in positioning the cursor at a desired position or "target" in the graphical user interface. Or, a turbulence sensation imposed on a joystick interface during a flight simulation game may cause the user object to shake, which in turn makes the airplane fly erratically since the airplane trajectory is based on locative signals derived from the position or motion of the user object. These undesired displayed effects can be referred to as "disturbances" due to their interfering effect on the position of a controlled graphical object or entity.
A different way to describe this problem is to view an actuated interface device as a user manipulatable object interfaced to a host computer through both input and output channels. The input channel transmits the locative data from the interface device to the host computer, where the data is used by the host to position simulated objects. The output channel transmits the force feedback sensations imposed on the user manipulatable object in response to host commands. Because the force feedback sensations (output) can disturb the user object and therefore disturb the sensor readings (input), the input and output channels are coupled. This coupling causes the problems outlined above, such as hindering a user's ability to accurately control a cursor or play a video game using the interface device.